Travis: failed to bind to port 11211 #10869

Looks like a spurious Travis failure in p2p-segwit.py here: https://travis-ci.org/bitcoin/bitcoin/jobs/254520908#L5356

2017-07-17 19:06:34.660901 Unable to bind to 0.0.0.0:11211 on this computer. Bitcoin Core is probably already running.

test_runner.py and test_framework.py are very careful to not re-use ports for p2p and rpc interfaces on different nodes/tests, so perhaps another process was bound to 11211. Googling for port 11211 shows that it's memcached's default port.

Should be easy to test whether port 11211 causes problems by pushing a branch with port_seed() changed.

Most intermittent failures with ports could be avoided by using UNIX sockets for testing, too bad that that didn't make it.

The most simple work around would be to stop picking 11211:

diff --git a/test/functional/test_framework/util.py b/test/functional/test_framework/util.py
index acca72aa8..43f689df5 100644
--- a/test/functional/test_framework/util.py
+++ b/test/functional/test_framework/util.py
@@ -164,5 +164,5 @@ def satoshi_round(amount):
 MAX_NODES = 8
 # Don't assign rpc or p2p ports lower than this
-PORT_MIN = 11000
+PORT_MIN = 11222
 # The number of ports to "reserve" for p2p and rpc, each
 PORT_RANGE = 5000

@jnewbery Do you think this issue is worth to tackle/keep open?

Setting 'Up for grabs'. Next steps, for anyone who wants this:

• confirm that it really is port 11211 that causes problems.
• fix using Marco's workaround or some other way.